This invention relates to a charging control apparatus for a vehicle for controlling generation of electric power from a vehicle's a.c. generator charging a battery, and more particularly to an apparatus of the kind described above which controls a field current of the generator so as to control the rate of increase in the field current when an electrical load is connected to the generator.
A charging control apparatus for a vehicle is disclosed in JP-A-59-83600 (corresponding to U.S. Pat. No. 4,459,489). According to the disclosed charging control apparatus, the fact that the output voltage of a vehicle's generator driven by an engine has dropped to a predetermined level (0.5 V) as a result of connection of a large electrical load to the generator is detected, and, in response to the detection of the voltage drop, the ratio of current having been supplied to the field winding of the generator before the connection of the electrical load is gradually increased. By so gradually increasing the field current of the generator, the load of the generator is gradually applied to the engine, so that the engine can be prevented from vibration or stalling.
This prior art charging control apparatus requires a first capacitor for detecting the mean conduction rate of the current supplied to the field winding of the generator, and a second capacitor to which the charge of the first capacitor is transferred when the drop of the output voltage of the generator to the predetermined level is detected. The voltage charged in the second capacitor is discharged through a resistor, and the output of the resistor is compared with a triangular waveform voltage to generate a signal used to gradually increase the current supply ratio up to 100%. The period of time required for gradually increasing the current supply ratio up to 100% is determined by the time constant given by the product of the capacitance of the second capacitor and the resistance of the resistor. Therefore, when the time constant of about several seconds is desired, the required capacitance value of the second capacitor is larger than a predetermined value (about 1 .mu.F). Also, the required capacitance value of the first capacitor is about ten times as large as that of the second capacitor in view of the requirement for transferring the charge of the first capacitor into the second capacitor.
Thus, large capacities are required for the first and second capacitors, resulting in a large size of the charging control apparatus. In other words, ceramic capacitors are required to act as these capacitors, and the first and second capacitors cannot be integrated into a hybrid IC together with other control elements.
Further, the prior art charging control apparatus requires comparing means including a capacitor, a resistor and a comparator so as to detect a drop of the output voltage of the generator due to connection of an electrical load, and this results inevitably in a large size of the apparatus.